Phenological variation of Rhizophora mangle and ground water chemistry associated to changes of the precipitation

Mangrove forests are vulnerable to long term changes of temperature and precipitation. In this study, we want to know if the precipitation regime significantly varies among years and seasons during a five-yr period (2006-2010) at the North of Laguna de Términos, Campeche, Mexico. In addition, we want to know how the salinity and the redox potential of the ground water of a monospecific mangrove forest of Rhizophora mangle are modified according to this variation. Finally, we describe the total litterfall, and the flowers and hypocotiles production of the studied mangrove and analyze these responses as a function of the environment variables. A repeated measures ANOVA showed that precipitation significantly varied among years and seasons (F=15.83, p<0.003; F=29.8, p<0.0001). The salinity and the redox potential were also significant effects of the same temporal variation (F=1003.25, p<0.0001; F=213.32, p<0.0001), as well as the total litterfall and the hypocotile production (F=39.35, p<0.001; F=8.74, p<0.025). Precipitation was directly proportional to the hypocotile production (r=0.43, p<0.005) and inversely proportional to the salinity ground water (r= - 0.36, p<0.02). The precipitation and the salinity play significant roles on the variation of the litterfall and the hypocotile production of the studied mangrove (R2= 0.85; p<0.05 and R2= 0.70; p<0.05). Our study suggests a resilient ability of R. mangle, whichallows it to tolerate seasonal and annual changes of the precipitation

Cambios de cobertura y uso del suelo (1979-2000) en dos comunidades rurales en el noroeste de Quintana Roo

El análisis de los cambios de cobertura y uso del suelo (ccus) en relación con las actividades humanas es esencial para entender y predecir la dinámica del paisaje. Se analizan los ccus en Solferino y San Ángel, dos comunidades rurales del noroeste de Quintana Roo, a partir de fotografías aéreas de 1979 y 2000, recorridos de campo y entrevistas para documentar la historia de uso del suelo. Contrario a la mayoría de estudios, se registró un aumento en la cobertura de selvas, proveniente principalmente de la regeneración de áreas quemadas, lo cual resalta el papel de los incendios como agentes de cambio de cobertura y la capacidad de recuperación de las selvas. El cambio en el uso del suelo favoreció ligeramente la deforestación en Solferino, debido en parte a una mayor disponibilidad de selvas para usos agropecuarios en las cercanías del poblado. En San Ángel se observó una mayor regeneración de selvas, debido en parte a una mayor deforestación previa, asociada a un gran aumento poblacional y a la implementación de programas federales de fomento a la ganadería. Se discuten los escenarios de cambio y las posibles repercusiones de las actuales tendencias institucionales, socioeconómicas y climáticas sobre los futuros ccus

Decomposition in tropical forests: a pan-tropical study of the effects of litter type, litter placement and mesofaunal exclusion across a precipitation gradient

1. Litter decomposition recycles nutrients and causes large fluxes of carbon dioxide into the atmosphere. It is typically assumed that climate, litter quality and decomposer communities determine litter decay rates, yet few comparative studies have examined their relative contributions in tropical forests. 2. We used a short-term litterbag experiment to quantify the effects of litter quality, placement and mesofaunal exclusion on decomposition in 23 tropical forests in 14 countries. Annual precipitation varied among sites (760-5797 mm). At each site, two standard substrates (Raphia farinifera and Laurus nobilis) were decomposed in fine- and coarse-mesh litterbags both above and below ground for approximately 1 year. 3. Decomposition was rapid, with >95% mass loss within a year at most sites. Litter quality, placement and mesofaunal exclusion all independently affected decomposition, but the magnitude depended upon site. Both the average decomposition rate at each site and the ratio of above- to below-ground decay increased linearly with annual precipitation, explaining 60-65% of among-site variation. Excluding mesofauna had the largest impact on decomposition, reducing decomposition rates by half on average, but the magnitude of decrease was largely independent of climate. This suggests that the decomposer community might play an important role in explaining patterns of decomposition among sites. Which litter type decomposed fastest varied by site, but was not related to climate. 4. Synthesis. A key goal of ecology is to identify general patterns across ecological communities, as well as relevant site-specific details to understand local dynamics. Our pan-tropical study shows that certain aspects of decomposition, including average decomposition rates and the ratio of above- to below-ground decomposition are highly correlated with a simple climatic index: mean annual precipitation. However, we found no relationship between precipitation and effects of mesofaunal exclusion or litter type, suggesting that site-specific details may also be required to understand how these factors affect decomposition at local scales.Comparative Tropical Biology FellowshipComparative Tropical Biology FellowshipMellon FoundationMellon FoundationU.S. National Science Foundation (NSF)NSF[DBI-0338143